QAM

About: QAM is a research topic. Over the lifetime, 7793 publications have been published within this topic receiving 102473 citations.

Increasing the QAM spectral efficiency

Abstract: In this paper the method of increasing the spectral efficiency of quadrature amplitude modulation by using the instantaneous phase of the carrier as an additional parameter information is substantiated.

Data transmission using carrierless qam

Abstract: Carrierless signals of first and second channels pass via filters having quadrature responses and are then added for transmission. A receiver uses adaptive filters (4, 5) which also need quadrature responses to separate the channels effectively. To accommodate misconvergence of the filters giving rise to (a) inverted responses, (b) differential delays, (c) similar or identical responses and/or (d) transposed responses, and hence incorrect decoding: (a) the transmitter and receiver may employ differential coding (25-32) in each channel, (b) the receiver may calculate (33) the group delay of its filters and correct any error, (c) the receiver may compare (34) the filtered signals and if similar replace one filter response with a quadrature response calculated (39) from the other and/or (d) the receiver may respond to a failure to recognize (43, 44) expected synchronization words by transposing (45, 46) the responses of the filters.

An Improved BER Calculation for Nonlinear Successive Interference Cancellation

Abstract: In this contribution, an algorithm for calculating the Bit Error Rate (BER) of a nonlinear Successive Interference Can- celler (SIC) in a Direct Sequence-Code Division Multiple Access (DS-CDMA) system was presented. The model of our algorithm was actually originated from a notion proposed by Frenger, et al. (1) for a Binary Phase Shift Keying (BPSK) DS-CDMA sys- tem. However by modifying that algorithm so as to exploit the characteristics exhibited by the nonlinear SIC, we managed to improve the accuracy of each user's computed BER. Furthermore, our modified algorithm can also be applied in certain anomalous conditions, such as imperfect recreation of a user's signal. Our improved algorithm is then further extended, in order to calculate the BER of each user for a 16 Quadrature Amplitude Modulation (QAM) DS-CDMA system. In all cases, it was shown that the BER for each user computed by our algorithm nearly matches with that obtained by simulation.

Performance Improvement of Multi-User MC-CDMA System Using Discrete Hartley Transform Mapper

Abstract: Future wireless communication systems must be able to accommodate a large number of users and simultaneously to provide the high data rates at the required quality of service. In this paper a method is proposed to perform the N-Discrete Hartley Transform (N-DHT) mapper, which are equivalent to 4-Quadrature Amplitude Modulation (QAM), 16-QAM, 64-QAM, 256-QAM, … etc. in spectral efficiency. The N-DHT mapper is chosen in the Multi Carrier Code Division Multiple Access (MCCDMA) structure to serve as a data mapper instead of the conventional data mapping techniques like QPSK and QAM schemes. The proposed system is simulated using MATLAB and compared with conventional MC-CDMA for Additive White Gaussian Noise, flat, and multi-path selective fading channels. Simulation results are provided to demonstrate that the proposed system improves the BER performance and reduce the constellation energy as compared with the conventional system.

Noncoherent Multiuser Massive SIMO for Low-Latency Industrial IoT Communications.

Abstract: In this paper, we consider a multiuser massive single-input multiple-output (SIMO) enabled Industrial Internet of Things (IIoT) communication system. To reduce the latency and overhead caused by channel estimation, we assume that only the large-scale fading coefficients are available. We employ a noncoherent maximum-likelihood (ML) detector at the receiver side which does not need the instantaneous channel state information (CSI). For such a massive SIMO system, we present a new design framework to assure that each transmitted signal matrix can be uniquely determined in the noise-free case and be reliably estimated in noisy cases. The key idea is to utilize a new concept called the uniquely decomposable constellation group (UDCG) based on the practically used quadrature amplitude modulation~(QAM) constellation. To improve the average error performance when the antenna array size is scaled up, we propose a max-min Kullback-Leibler (KL) distance design by carrying out optimization over the transmitted power and the sub-constellation assignment. Finally, simulation results show that the proposed design outperforms significantly the existing max-min Euclidean distance based method in terms of error performance. Moreover, our proposed approach also has a better error performance than the conventional coherent zero-forcing (ZF) receiver with orthogonal training for cell edge users.